#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#include <arpa/inet.h>
#include <sys/socket.h>

#define BUF_SIZE 30
void error_handling(char *msg);


int main(int argc, char *argv[])
{
    int serv_sock;
    char msg[BUF_SIZE];
    int str_len;
    socklen_t clnt_adr_sz;
    struct sockaddr_in serv_addr;
    struct sockaddr_in clnt_addr;
    if (argc != 2) {
        printf("Usage: %s <port>\n", argv[0]);
        exit(1);
    }

    serv_sock=socket(PF_INET, SOCK_DGRAM, 0);
    if (serv_sock == -1) {
        error_handling("UDP socket creation error");
    }

    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(atoi(argv[1]));

    if (bind(serv_sock, (struct sockaddr *)&serv_addr, sizeof(serv_addr)) == -1) {
        error_handling("bind() error");
    }


    while (1) 
    {
        clnt_adr_sz = sizeof(clnt_addr);
        str_len = recvfrom(serv_sock, msg, BUF_SIZE, 0,
            (struct sockaddr *)&clnt_addr, &clnt_adr_sz);
        sendto(serv_sock, msg, str_len, 0,
            (struct sockaddr*)&clnt_addr, clnt_adr_sz);
    }

    close(serv_sock);

    return 0;
}


void error_handling(char *msg)
{
    fputs(msg, stderr);
    fputc('\n', stderr);
    exit(1);
}
